rpmostreepayload: Do /sysroot mount non-recursively

In rhinstaller#903 we
changed all of rpmostreepayload's internal mounts to be
recursive to fix `/boot/efi`.  And indeed all should be recursive,
except one - the `/sysroot` mount.  By asking for that to be
recursive we've created a loop.

I noticed a while ago that the output of `findmnt` during an install was insane
(the deployment directory was visible twice, etc.), but never debugged it. It
turns out this was the cause.

Fixing this makes the mounts look a lot more sane, and will help
for future work I have for `/var` mounts.

pyanaconda/payload/rpmostreepayload.py

@@ -248,7 +248,6 @@ def prepareMountTargets(self, storage):
         # Set up bind mounts as if we've booted the target system, so
         # that %post script work inside the target.
         binds = [(iutil.getSysroot() + '/usr', None),
-                 (iutil.getTargetPhysicalRoot(), iutil.getSysroot() + "/sysroot"),
                  (iutil.getTargetPhysicalRoot() + "/boot", iutil.getSysroot() + "/boot")]
 
         # https://github.com/ostreedev/ostree/issues/855
@@ -275,6 +274,12 @@ def prepareMountTargets(self, storage):
                                            ["--rbind", src, dest])
             self._internal_mounts.append(src if is_ro_bind else dest)
 
+        # And finally, do a nonrecursive bind for the sysroot
+        self._safeExecWithRedirect("mount",
+                                   ["--bind", iutil.getTargetPhysicalRoot(),
+                                    iutil.getSysroot() + "/sysroot"])
+        self._internal_mounts.append(iutil.getSysroot() + "/sysroot")
+
         # Now, ensure that all other potential mount point directories such as
         # (/home) are created.  We run through the full tmpfiles here in order
         # to also allow Anaconda and %post scripts to write to directories like